Rolling bearings to be used in a turbopump for rocket engines are used under environments of high speed rotation in liquid propellant. In particular, in a case of using the rolling bearings in liquid hydrogen or liquid oxygen, the rolling bearings are exposed to ultra-low temperatures. Thus, fluid lubricants such as oil and grease for normal rolling bearings cannot be employed. Further, when the rolling bearings are used in high speed rotation, high hoop stress is applied to the cages, and hence the cages need to have high specific strength.
For example, in JP 02-20854 B, there is disclosed a cage made of a fiber-reinforced composite obtained by impregnating woven fabric made of a reinforced fiber such as a glass fiber with a solid lubricant such as PTFE. This cage is formed by machining the fiber-reinforced composite, and hence strands of the cut glass fiber are exposed on surfaces of the cage. When the strands of the glass fiber come into contact with rolling elements, contact between the rolling elements and the solid lubricant is hindered. As a result, the solid lubricant may not be sufficiently transferred onto the rolling elements, which causes a risk of deterioration in reliability of resistance against frictional abrasion. As a countermeasure, according to JP 02-20854 B, after the machining of the fiber-reinforced composite, the strands of the glass fiber, which are exposed on the machined surface portions, are removed through dissolution with a surface treatment agent (hydrofluoric acid).